1. Field of the Invention
This invention relates to a tetraazaannulene cobalt complex compound (hereinafter referred to Co-TAA) useful as an oxygen reduction catalyst and a method for the preparation of the Co-TAA.
2. Description of the Prior Art
Various kinds of oxygen reduction catalysts have been known. Especially, platinum has been well known as an oxygen reduction catalyst because of the superior catalytic properties. However, it is difficult to practically employ platinium as a catalyst in a fuel battery because platinum is expensive and a rare metal. Therefore, the development of new catalysts having a low oxygen reduction voltage and a high catalytic activity have been desired and made. However, the catalysts which can take the place of platinum have not been found.
The Co-TAA having the formula (VII); ##STR2## is reported as an oxygen reduction catalyst having a high activity in F. Beck et al, Z. Naturforsch. 28a, 1009-1021(1973), and DE-OS No. 20 46 354. However, the catalyst life of the Co-TAA of the formula (VII) is short and, in addition, the catalyst activity is not satisfactory.
Further, the Co-TAA having the formula (VIII); ##STR3## is reported in Y. Nishida et al, Bulletin of the Chemical Society of Japan, Vol. 50(9), 2485-2486 (1977). There is no description relating to the oxygen reduction catalyst properties of the Co-TAA of the formula (VIII) in the report. The inventors of this invention have produced the Co-TAA of the formula (VIII) to measure the catalytic properties, and found that the catalyst activity is insufficient though the catalyst life is long.
A method for the preparation of the Co-TAA is described in Y. Nishida et al, Journal of Coordination Chemistry, Vol. 9, 161-166 (1979). This method, however, has a defect that the reaction procedures and the aftertreatments are difficult due to the use of sulfur and acetyl hydroperoxide in the production of the starting material, that is, dithiolium hydrogensulfate. Further, this method has such defects that the yields of the tetraazaannulene and the Co-TAA are low, that the purity of the Co-TAA is also low and that the purification of the Co-TAA is difficult.